1. Field of the Invention
The present invention generally relates to a method and apparatus for automatically monitoring objects and, more particularly, but not by way of limitation, to an improved automatic monitoring method and apparatus utilizing a direct proximity technique.
2. Brief Description of the Prior Art
In the past, various systems and devices have been proposed for monitoring at a central location the movement, position, location or the like of various objects, such as vehicles, people and the like, for example. With respect to systems and apparatus designed to monitor the location of vehicles, such systems have been referred to in the art generally as "Automatic Vehicle Monitoring" (AVM) systems.
One automatic vehicle monitoring system was disclosed in the U.S. Pat. No. 3,714,573, issued to Grossman. In general, the system disclosed in the Grossman patent utilized a pulse ranging technique and systems of this type are sometimes referred to in the art as "multilateration" since such systems generally require the simultaneous reception and processing of signals from several remote stations. Further, it has been found that systems of this type generally encounter multipath problems and the equipment costs are relatively high since computational equipment is required in addition to the automatic reporting and radio equipment. The Mitre Corporation, "Urban Field Tests of Four Vehicle Location Techniques", Report No. UMTA-VA-06-0012-73-1, April 1973, McLean, Virginia.
One other automatic vehicle monitoring system utilized in the past was generally referred to in the art as a "dead reckoning" type of system. In this type, a relatively small navigation apparatus was located on the vehicle and utilized to report vehicle direction and distance and, in some instances, vehicle acceleration to a central computer. In general, a dead reckoning type of system required communication between the monitored vehicle and the central computer at frequent intervals and periodic updating because errors would continuously accumulate unless reset manually or via some logic network.
The dead reckoning type of system and the pulse ranging type of system also are considered as "fail hard" systems; that is, utilizing either of these systems, the complete system became non-operational when any particular component unit failed or malfunctioned, except the system location reporting link.
On other additional automatic vehicle monitoring system utilized what was sometimes referred to as a "proximity" method or approach. In the systems utilizing the proximity method, an electronic unit was located at predetermined positions along a fixed, known route.
It should be noted that there are generally considered to be two basic types of proximity methods: one being sometimes referred to as "direct proximity"; and the other being sometimes referred to as "inverse proximity". The inverse proximity method utilizes electronic units located at predetermined locations for receiving data from vehicles when the vehicles are positioned within a predetermined distance from the particular electronic units, such a method being disclosed in the U.S. Pat. No. 3,586,161, issued to Paul, for example, the inverse proximity method is particularly suitable for applications requiring a relatively small number of electronic units positioned at fixed locations since relatively inexpensive coding devices can be placed on the objects to be monitored. However, in those applications wherein a relatively large number of objects are to be monitored, the inverse proximity method has been found to be relatively costly and, in most instances, systems employing the inverse proximity method are considered to be capacity limited since all of the monitored vehicle data must be communicated via a common data link. The direct proximity method is not considered to be capacity limited in a manner just mentioned in connection with the inverse proximity method. Applications employing the direct proximity method generally utilize an electronic unit located at predetermined positions and a relatively large number of monitored objects utilize the same electronic units, examples of systems employing the direct proximity method being disclosed in the U.S. Pat. Nos. 3,644,883 and 3,718,899, issued to Rollins, and the U.S. Pat. No. 3,757,290, issued to Ross, for example.
In the past, most applications employing the direct proximity method have been constructed to operate in relatively high frequency ranges, such as greater than one hundred (100) MHz, for example, which limited the area covered by each electronic unit positioned at the predetermined locations in order to provide acceptable resolution, such systems also utilizing equipment requiring relatively large amounts of electrical power for operating the electronic units positioned at predetermined locations which necessitated permanent electrical connections. Systems employing the direct proximity method have generally required the polling of the monitored objects or vehicles resulting in either the utilization of a relatively expensive and complicated timer in the monitored objects or in the central computer apparatus or, in some applications, in both the monitored objects and the central computer apparatus, or resulting in the utilization of a relatively fast polling rate. Further, systems employing the direct proximity method have generally required a dedicated radio channel, thereby increasing the system costs.
Various types of automatic vehicle monitoring systems have been described in the following publications: M. L. Reiss, et al., "Feasibility Study, Automatic Vehicle Identification System", June 1969, PB 185 387, NTIS, U.S. Department of Commerce, Springfield, Virginia. Martin Lukes, Raymond Shea, "Monitor-CTA", May 1973, Final Report, UMTA, Department of Transportation, Washington, D.C. Dr. Richard C. Larson, "Urban Police Patrol Analysis", 1972, Massachusetts Institute of Technology. R. Buck, et al., "Analysis and Comparison of Some Automatic Vehicle Monitoring Systems", July 1973 Interim Report, Department of Transportation, Washington, D.C. Raymond L. McLean, "Vehicle Location and Status Reporting System (LOCATES)", Report No. APD TECH-72-101, Phase I Final Report, 1972, City of Montclair Police Dept., Montclair, California. Stephen Riter, "Proceedings of a Conference on Automatic Vehicle Monitoring", Report No. 731, 1973, Texas A & M University, College Station, Texas.